Exemplary embodiments of the invention relate to the art of turbomachines and, more particularly, to a method of refurbishing a seal land on a turbomachine turbine transition piece.
In general, turbomachines, particularly gas turbine engines, combust a fuel/air mixture to release heat energy to form a high temperature gas stream that is channeled to a turbine section via a hot gas path. More specifically, a compressor compresses incoming air to a high pressure. The high pressure air is delivered to a combustion chamber to mix with fuel and form a combustible mixture. The combustible mixture is then ignited to form a high pressure, high velocity gas that is passed through a transition piece into a first stage of a turbine. The turbine converts thermal energy from the high temperature, high velocity gas stream to mechanical energy that rotates a turbine shaft. The turbine shaft is coupled to and drives the compressor and also other machinery such as an electrical generator.
In a typical gas turbine, an air duct surrounds the transition piece and delivers cooling air from the compressor. Joints between the transition piece and the turbine must be properly sealed. That is, the combustion process creates a pressure differential between the hot gases passing into the turbine and the cooling air supplied by the compressor. Without proper sealing between the transition piece and the turbine, compressor cooling air could pass into the turbine resulting in performance and efficiently losses. The seal must be able to withstand the high temperatures of the engine while at the same time remaining flexible so as to accommodate vibrations/deflections and/or travel of the transition piece due to thermal expansion and turbine starts and stops. Over time, the vibrations/deflections and/or travel cause the seal to abrade a seal land portion of the transition piece resulting in wear. When the wear is significant, the seal land must be refurbished.
At present, many turbines are taken off line every 12,000 or so hours of run time or combustion intervals (CI) in order to perform inspection/routine maintenance. During the CI, seal lands are inspected and, if out of tolerance, refurbished. Currently, a seal land is refurbished by applying a new layer of material on the seal land. The new layer of material, typically a nickel based alloy similar to that used in the construction of the transition pieces, is applied in layers by a welding process. While the new layer of material enables the transition piece to return to service, the new layer will erode as fast as, or faster, than the original seal land. Moreover, there are a finite number of refurbishing cycles that can be performed before the seal land will become fatigued. Refurbishing a seal land in this manner is very expensive, requiring up to 300 hours/set, and only extends the life of a transition piece a finite period.